Electrical parameters of a symmetrical hot carrier solar cell double heterostructure with metallic absorber layer and high-pass energy filters are calculated within thermionic emission theory. An efficiency limit of 73% is predicted for infinite characteristic cooling time and full solar concentration. Carrier cooling is treated within linear thermal conductivity model. Heat loss through carrier cooling in the absorber layer depends not only on the characteristic cooling time, but also on the specific volumetric heat capacity of the carrier gas and on the thickness of the absorber layer. Optimal absorption of light together with small thermal loss to the lattice require high carrier mobility in the absorber layer.